1. Field of the Invention
The present invention relates to a plastic lens, a lens module and a lens injection mold.
2. Description of the Related Art
In general, plastic optical lenses are used in the form of a lens module. The lens module is manufactured in such a manner that an optical lens is formed by injection molding or the like and is then assembled in a unit receiving the lens (barrel, housing, or the like) automatically or by a user.
In recent years, a subminiature lens module has been used in various applications such as in a cellular phone, a webcam and a security camera. In response to high pixel requirements due to the improved integration of a sensor, precise assembly is required so as to accurately adjust the position of an optical axis in the formation of a precision lens having a minimum error in shape and a module using the precision lens.
A plastic lens, manufactured by injection molding, has a non-axisymmetric shape since a gate portion thereof is cut after the injection molding. When such a non-axisymmetric lens is assembled in a barrel by a press-fitting process, it is contracted and deformed so that a center of an optical axis of an effective aperture portion is altered.
A conventional lens, manufactured by injection molding, contracts asymmetrically due to its non-axisymmetric shape since it is subjected to contraction load inside a barrel while a gate-cut portion thereof is not affected by the load. Particularly, an error in shape may be caused in the direction of the gate-cut portion and the direction perpendicular thereto, so that precise formation is difficult.
Also, when an outer circumferential surface of a circular rib portion is pressed and fitted into an inner circumferential surface of a barrel, excessive press-fitting force is applied thereto. This causes tilting and plastic deformation of the lens and the barrel receiving the lens during the press-fitting process.